Polyolefin resins such as polypropylene and polyethylene are widely used because of being inexpensive and excellent in e.g., moldability, chemical resistance, water resistance, electrical property and safety. However, since polyolefin resins are hydrophobic materials with low polarity, adhering the polyolefin resins to polar resins such as acrylic resins, polyester-based resins, polycarbonate-based resins and ABS resins is difficult. Thus, it is now difficult to laminate the polar resins on the surface of the polyolefin resins and to decorate the surface of the polyolefin resins with an ink or a coating material.
A resin adhesive to such polyolefin resins that has been known is, for example, acid-modified polyolefin resin such as a resin modified with an unsaturated carboxylic acid (Patent Document 1); a chlorinated polyolefin resin, an acrylic sticky adhesive, a styrene-ethylene-propylene-styrene block copolymer rubber (Patent Document 2); a styrene-butadiene-styrene block copolymer rubber (Patent Document 3); or a modified block copolymer which is a hydrogenated product of a styrene.conjugated diene.styrene-based block copolymer graft-copolymerized with maleic anhydride (Patent Document 4).
Still, even with the use of these materials, it is now difficult to allow the polyolefin resins to exhibit sufficient adhesion to a wide range of materials ranging from low-polarity polyolefin resins to polar resins such as acrylic resins, polyester-based resins, polycarbonate-based resins and ABS resins, particularly at the time of application procedure conducted at low temperature of about 100° C.
Meanwhile, as a novel decorating technique, a method has been proposed in which a design film (decorative film) is attached to molded articles with various forms and the molded articles are thus decorated (Patent Documents 5 and 6). This method, which can simplify coating step, increases added value and decreases environmental load, has been already used for e.g., housings of household appliances and automobile interior and exterior parts.
Since base materials of the design layer are generally resins with high polarity such as urethane-based resin and acrylic resin, in order to attach the decorative film to a molded article of the polyolefin resin such as polypropylene, a bonding layer is required to adhere the polyolefin resin to the design layer with high polarity such as urethane-based resin and acrylic resin.